1. Field of the Invention
The present invention relates to an exhaust device of a multi-cylinder engine including a catalyst arranged to purify an exhaust gas discharged from an outboard motor multi-cylinder engine.
2. Description of Related Art
One example of an exhaust device of a multi-cylinder engine is described in Japanese Published Unexamined Patent Application No. 2005-22509. This exhaust device is provided for a 4-cylinder engine for a two-wheeled motor vehicle, and includes an exhaust pipe which collects exhaust passages of cylinders in one passage. A catalyst is provided on the upstream side of the collecting portion in the exhaust pipe.
On the other hand, in U.S. Patent Application Publication No. 2008/022669A1, an example of an outboard motor is disclosed. This outboard motor includes an engine which supports a crankshaft in an up-down direction, a casing positioned below the engine, and a cowling surrounding the engine. The engine is a multi-cylinder engine. The outboard motor includes an exhaust pipe which connects the engine and a main exhaust passage inside the casing for preventing exhaust interference among cylinders of the engine.
The lower end of the crankshaft is connected to a drive shaft. The drive shaft is housed in the casing and extends in an up-down direction. The lower end of the drive shaft is coupled to a propeller supported rotatably on the lower end of the casing.
The main exhaust passage is formed to penetrate the inside of the casing in the up-down direction. An inlet end of the main exhaust passage is connected to exhaust outlets of the cylinder heads via an exhaust pipe. Also, the outlet end of the main exhaust passage opens in water at the shaft center of the propeller.
The exhaust pipe has a tubular portion forming exhaust passages of the cylinders. The plurality of exhaust passages are connected commonly to an exhaust chamber and collected together. The exhaust chamber is connected to the main exhaust passage.
The tubular portion includes an exhaust manifold portion positioned between two cylinder heads. The tubular portion further includes a horizontal pipe portion extending from the exhaust manifold portion. In this horizontal pipe portion, two catalysts are disposed in series.